California Black Worms Nikki Metzger

Question: Do California black worms regenerate faster in the light or in the dark?

The fragmentation, during which black worms divide into two or more fragments. Each fragment then undergoes rapid regeneration to form a whole new worm. The tail end of the blackworm is specialized for gas exchange. While a black worm is foraging for food with its head, it stretches its tail to the surface of the water. The tail breaks the surface tension of the water and forms a right angle. Exchange of oxygen and carbon dioxide occurs between the outside air and the pulsating blood vessel that lies just below the upper epidermis. The anterior (head) end differs from the posterior (rear) end of a blackworm (in a fragment as well as in an unfragmented worm) in several ways. First, the blood in the dorsal (upper) vessel always travels toward the head. The anterior end is normally wider, blunter, and more pigmented than is the posterior end. The anterior end is usually more active and probing. Research:

In earthworms, leeches, and other relatives of the blackworm, certain internal organs are always found within a particular range of body segments. This is not the case with blackworms. In fact, with the blackworms, many of the middle and posterior segments are able to transform themselves into segments similar to those at its anterior end. This is related to the blackworm’s capacity for asexual reproduction and regeneration. Lumbriculus variegatus, can be cut into several fragments and it won’t die or even bleed. Instead, it regenerates a new head or tail, or both, from the various pieces. What’s more amazing is that the blackworm is not a rare animal living in some faraway place. Usually no more than 10 centimeters long, this worm lives in shallow edges of ponds, marshes, and lakes throughout North America and Europe.

Hypothesis If I put twenty-five worms in the light and twenty-five in the dark, then the worms in the light will regenerate faster.

Independent Variable: Light vs. Dark Dependent Variable: Amount of regeneration (number of segments)

Controls Type of worm Time Containers Cutting Procedure

Material List Worms Petri dish Transparency for cutting Pipette Microscope slide Containers Water

Procedure 1. Cut approximately 25 California Black Worms in half using a cutting tool made from an overhead transparency. 2. Allow the worms to set over night. 3. Number each vial 1 to Put each piece of worm into a vial. 5. Put vials #1-25 in the dark and vials #26-50 in the light. 6. On Day 6, use a pipette to carefully remove a worm from the vial and place it on a microscope slide. 7. Focus on the worm and count each new segment that has formed. (the regenerated segments appear light in color) 8. Repeat Steps 6 and 7 for each worm. 9. Observe each worm every 4 days for 3 weeks.

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